1. Field of the Invention
The present invention relates to an intake control system and method for an internal combustion engine, for adjusting an intake air amount by changing the lift of an intake valve using a variable intake lift mechanism, and adjusting intake pressure using a throttle valve.
2. Description of the Related Art
Conventionally, there is known an intake control system for an internal combustion engine as disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2008-196474. The internal combustion engine is equipped with a variable intake lift mechanism for adjusting an intake air amount by continuously changing the lift of an intake valve, and a throttle valve for adjusting intake pipe pressure by changing the opening of the throttle valve. In the intake control system, a target intake air amount is calculated according to operating conditions of the engine, and based on the calculated target intake air amount, the lift of the intake valve is changed, whereby the intake air amount is controlled. Further, the opening of the throttle valve is set according to the target intake air amount to thereby secure the target intake air amount. Further, the intake pipe pressure (absolute pressure) on the downstream side of the throttle valve and atmospheric pressure are detected, and an intake pipe gauge pressure is calculated based on the detected intake pipe pressure and atmospheric pressure. Then, the opening of the throttle valve is corrected by feedback control such that the gauge pressure becomes equal to a target gauge pressure, whereby the intake pressure is controlled.
In the conventional intake control system, however, when the target intake air amount is changed, there occurs an inevitable delay before the intake air amount actually becomes equal to the target intake air amount. On the other hand, the opening of the throttle valve is basically set according to the target intake air amount. Therefore, especially during a transient operation of the engine in which the target intake air amount is largely varied, the delay of the actual intake air amount from the target intake air amount has such an influence on the intake pressure to change the same. Since the opening of the throttle valve is corrected such that the changed intake pressure becomes equal to the target gauge pressure, it is impossible to accurately control the gauge pressure to the target gauge pressure.